Robin Shelton

Research Interests

Massive clouds of gas are orbiting around and, occasionally, plummeting into our Galaxy at speeds in excess of 200,000 miles per hour. If your eyes could see radio-waves or ultraviolet light, you would see that these clouds cover 2/3 of the sky. You would also see a variety of shapes, ranging from tiny dots to a 100,000 lightyear long streamer of clouds that weighs 10 million times the mass of the Sun. One of my research goals is to understand these clouds, called High Velocity Clouds (HVCs) and how they affect our Galaxy, the Milky Way. My research group uses computer clusters in the Georgia Advanced Computing Resource Center to simulate the hydrodynamic interaction between cloud gas and the gas in our own Galaxy. You can see one of our simulations here. Through these simulations, we've determined how mixing between cloud gas and hot gas in our Galaxy's outskirts heats up the cloud gas, fragments it, and, ultimately, causes it to merge with our Galaxy. Our simulational results compare well with ultraviolet observations of cloud gas and provide a new explanation for semi-hot gas in our Galaxy's outskirts (the halo).

The gas that is already in our Galaxy has been studied for several decades. From such work, we know that Galactic gas is the material from which new stars form and the material into which dying stars eject their ashes. We also know that the gas is most concentrated in a pancake-shaped disk that forms the spine of the Milky Way and least concentrated above and below the disk, where our Galaxy's gas blends with sparce intergalactic gas. My group studies the hottest gas in our galaxy, material that is about 1 to 2 million degrees Fahrenheit (roughly 1/2 to 1 million degrees Celsius). At these temperatures, the atoms in the gas glow brightly in ultraviolet and X-ray light. My group has a history of observing and analyzing the ultraviolet and X-ray photons and of using computers to simulate the interstellar gas. A small sample of our recent results follows. We have determined the quantity and temperature of hot gas in the halo of our galaxy by analyzing data taken by the X-ray Multi-Mirror observatory. We then compared these numbers with simulations made by our collaborators, finding that the hot halo gas was probably heated by the energy ejected into the halo from stars, most of which were in the disk of our galaxy. Using data from another X-ray telescope, the Suzaku telescope, we may have found the highest supernova remnant (an enormous bubble left behind after a star explodes) ever observed. Also, by comparing observations made of the same directions on the sky, but made at different points in time, we have shown that the solar heliosphere erratically produces X-rays. A selection of our X-ray observations can be seen here.